The present invention relates generally to dock leveling equipment and, more particularly, to a recycle system for dock levelers which helps to ensure that the lip of the dock leveler is properly moved into its retracted or pendant position before the dock leveler is moved into its cross-traffic or stored position.
Dock levelers are utilized to compensate for height differences between a dock platform and the bed of a vehicle parked adjacent the dock, and to form a bridge therebetween so that personnel and moving equipment may readily move on and off the vehicle during loading and unloading operations. Typical dock levelers includes a dockboard or deck which is pivotally hinged at its back edge to vary the height of the dock leveler, and an extension plate or lip which is pivotally hinged at the deck front edge to span the distance between the rear end of the vehicle bed and the outer front edge of the deck. In use, the lip moves relative to the front edge of the deck between a retracted or pendant position, to a range of extended, operative positions, including operative positions in which the lip extends from the front edge of the deck and rests upon and is supported by the bed of the parked vehicle. The lip may also be substantially coplanar with the upper surface of the deck when in an extended, operative position. In this way, the lip spans the gap between the rear edge of the vehicle bed and the front edge of the deck.
To move the lip from the retracted or pendant position to the extended operative position, the deck is normally pivoted upwardly a sufficient amount so that the lip can swing outwardly to an extended position without obstruction from the parked vehicle. A variety of powered means may be employed for both moving the deck and extending the lip, including hydraulic cylinders, linear actuators such as screw drives, air bags, etc. Once the lip has cleared the vehicle, the deck and the extended lip are pivoted downwardly as a unit until the extended lip rests upon the bed of the vehicle in the extended operative position. Once the loading/unloading operation is complete, it is desirable to return the leveler from this position to a xe2x80x9ccross-trafficxe2x80x9d or stored position where the deck is coplanar (and forms an extension of) the floor of the loading dock, and the lip is in its pendant position. The leveler may be returned to the cross-traffic position by the operator raising the deck.
As the deck is raised, the lip falls by gravity toward the pendant position. Once it is fully pendant, the operator can release the raise control and allow the deck and pendant lip to float downward to the cross-traffic position, in which the pendant lip is typically received within and supported by a fixed supports referred to as xe2x80x9clip-keepers.xe2x80x9d Such operator-controlled restoration of the leveler to a cross-traffic position is often referred to as xe2x80x9clip retractionxe2x80x9d as the lips is retracted from an extended to a pendant position during the movement.
On occasion, however, a trailer may depart without the operator performing lip retraction and restoring the leveler. If this occurs, the deck and lip float down to the deck""s lowest-most position of rotation (it xe2x80x9cbottoms-outxe2x80x9d), i.e. angled downwardly from its rear hinge beneath the level of the surrounding floor, and the lip then falls by gravity toward a pendant position. The same result occurs when a leveler is cycled to extend the lip, but the absence of a trailer allows the deck and lip to float all the way down. This creates the potential hazard of a so-called xe2x80x9cvoid in the floorxe2x80x9d since the deck and surrounding floor are not co-planar. A solution to this problem of creating a void in the floor where lip retraction is not performed is providing the leveler with an xe2x80x9cautomatic recyclexe2x80x9d or xe2x80x9cautomatic return to dockxe2x80x9d mechanism, which automatically returns the leveler to a cross-traffic position.
In one conventional type of recycle mechanism, the deck is automatically raised whenever the deck is sensed to be below a predetermined angle (typically a position close to being bottomed-out). This angle is determined, for example, by means of mercury switches or proximity switches. In such a system, once the deck angle is beyond the predetermined position, the deck is raised, allowing the lip to fall pendant. A detecting means (typically the same mercury switch or a timer) determines when the deck is above a certain anglexe2x80x94a deck angle determined to be high enough to have allowed the lip to fall completely pendantxe2x80x94at which time, power to the means lifting the deck is shut off, and the deck and pendant lip are allowed to float down to a cross-traffic position. Thus, such systems automatically recycle whenever the deck is at or near its lowest-most point of rotation. Such systems are limited in application, however. Trailers are often disposed below the height of the dock floor, requiring that the leveler deck be angled downward. The weight of cargo or material handling equipment being added to the trailer can force the trailer and the deck lower. This may cause the deck to move low enough to actuate the recycle mechanism, meaning that the leveler will recycle in the midst of the loading or unloading operationxe2x80x94a potentially dangerous proposition for the unwary dock worker. Accordingly, levelers employing this type of recycle system usually include a manual override switch that de-activates recycle to allow below-dock use. Unless that manual override is then re-set following servicing of the below-dock trailer, this important safety feature will remain disabled indefinitely.
Another conventional type of recycle system is actuated only by the relative angular position of the lip. In one example of such a system, a linear rod reciprocates as the lip extends and retracts (indeed- in the case of a lip powered by a hydraulic cylinder, the rod is directly coupled to the piston rod of the cylinder that actuates the lip). An actuating member, such as a metal tab, is connected to the rod and the linear position of the tab is thus indicative of lip angle. A mechanical switch is fixed adjacent to the path followed by the actuating member, and is engaged by the member during certain portions of its travel. The switch includes an activated position, and when the switch is in this position, power is provided to the deck which causes the deck to raise. Accordingly, the switch is designed and disposed so that it is only activated when the lip is moving from an extended toward a retracted position. Moreover, the switch is disposed and constructed such that the lip must first extend past a certain angle such that the actuating member moves over and past the switch before the switch can move to the activated position and provide power to raise the deck. Toward that end, the switch includes some lost motion wherein it can be engaged by the actuating member as the lip extends without being activated.
Thus, in operation, as the lips is extended, that actuating member moves past the switch. As the lips subsequently falls, following trailer departure, the actuating member again engages the switchxe2x80x94this time causing the deck to raise. The deck continues to raise as the actuating member continues to move over and be in contact with the switchxe2x80x94until the lip is nearly pendant. At this point, the actuating member loses contact with the switch, and the un-powered deck can float down to the cross-traffic position with the lip pendant. This system has the significant advantage of being capable of use in below-dock conditions without the need for a manual override, since recycle is a function of lip angle, as opposed to deck position. At the same time, this system requires careful adjustment. The actuating member must be sized and positioned to engage the switch long enough for the lip to fall pendant as the deck raises while also being sized and positioned to avoid setting up recycle for the small lip extensions sometimes required for below-dock end-load situations where it is desired to lower the leveler below-dock without allowing the lip to engage the trailer. Further, the switch must include some lost motion to allow recycle set-up only for full lip extension. Moreover, the sensitive adjustments of the actuating member and the switch need to be maintained in the somewhat harsh and rugged environment of a loading dock.
There is thus provided a recycling control system for a dockleveler including a pivotally mounted deck, a powered lifting mechanism for raising the deck, and a lip pivotally mounted to the deck for movement between pendant and extended positions, in which the control assembly includes a lip-position member couplable to the lip for movement therewith such that the position of the lip-position member is indicative of lip position, a switch couplable to the lifting means and operable to a first condition wherein power is provided to the lifting means, and operable to a second condition wherein power is not provided to the lifting means, and an actuator disposed on the lip-position member for movement relative thereto between at least a first position where the actuator operates the switch to the first condition, and a second position where the switch can be operated to the second condition, the actuator being disposed to move between the first and second positions as the lip moves toward the pendant position.